This invention relates generally to the control of an automotive transmission or the like. More particularly, it relates to improved shift control apparatus for a multiple speed, sliding gear manual transmission.
In recent years there have been many improvements in automotive drive trains, including improvements relating to control apparatus for shifting manual transmissions. Generally, for transmissions incorporating five forward speed ratios and a reverse speed ratio, the shift control apparatus provides three crossover positions for the shift stick. Each crossover position selects an appropriate shift fork, which may be moved longitudinally to engage two gear ratios. Thus, of the three crossover positions the first selects the first and second forward speed ratios, the second selects the third and fourth forward speed ratios, and the third selects the fifth forward and reverse speed ratios. Because longitudinal movement of the same shift fork in opposite directions engages either fifth or reverse, it is possible that reverse may be engaged inadvertently during the five-four downshifting operation. To prevent inadvertent reverse engagement, prior shift control apparatus has been designed to require that the shift stick be moved upwardly or downwardly before shifting into reverse, or alternatively that a special lever be moved prior to movement of the shift stick to engage reverse. Such apparatus has the disadvantage of involving complicated mechanisms and requiring some operator skill in the shifting operation.
Other prior apparatus is disclosed in U.S. Pat. No. 3,866,488 issued Feb. 18, 1975. As disclosed therein, three longitudinally movable shafts are selectively engageable by crossover movement of a shift stick. Longitudinal movement of the gear shift stick causes longitudinal movement of the selected shaft for effecting engagement of the appropriate gear. An inhibiting mechanism incorporating a single spring is provided to indicate the position of the shift stick vis-a-vis the five-reverse shaft. One disadvantage of this arrangement is that it requires the use of another shaft and the interlock in order to prevent an inadvertent shift into reverse. Another disadvantage of this arrangement is that the signal provided by the inhibiting mechanism may not be adequate.
Still other prior apparatus is disclosed in U.S. Pat. No. 3,929,029 issued Dec. 30, 1975. As disclosed therein, first and second shift rails are connected by a linkage mechanism. A shift stick is connected to the first shift rail such that movement in one direction causes rotation and movement in another direction causes longitudinal sliding of this shift rail. Motion of the first shift rail is transmitted through the linkage mechanism to the other shift rail so as to provide opposite rotation and longitudinal sliding thereof. One disadvantage of this arrangement is that it results in a shift pattern which is at variance with the shift pattern generally accepted in the automotive industry.